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Under-water superoleophobicity of fish scales.

Waghmare PR, Gunda NS, Mitra SK - Sci Rep (2014)

Bottom Line: We have identified the distinct chemical signatures that are responsible for such large contact angle, thereby making fish scale behave highly superoleophobic inside the water medium.In absence of the mucus layer, it is found that the contact angle decreases quite dramatically to around 150°, making it less oleophobic, the degree of such oleophobicity can then be contributed to its inherent hierarchical structures.Hence, through this systematic study, for the first time we have conclusively shown the role of the fish's mucus layer to generate superoleophobicity and negate the common notion that hierarchical structure is the only reason for such intrinsic behavior of the fish scales.

View Article: PubMed Central - PubMed

Affiliation: University of Alberta, Edmonton, Alberta, Canada.

ABSTRACT
Recent surge in the development of superhydrophobic/superoleophobic surfaces has been motivated by surfaces like fish scales that have hierarchical structures, which are believed to promote water or oil repellency. In this work, we show that the under-water oil repellency of fish scales is entirely due to the mucus layer formation as part of its defense mechanism, which produces unprecedented contact angle close to 180°. We have identified the distinct chemical signatures that are responsible for such large contact angle, thereby making fish scale behave highly superoleophobic inside the water medium. In absence of the mucus layer, it is found that the contact angle decreases quite dramatically to around 150°, making it less oleophobic, the degree of such oleophobicity can then be contributed to its inherent hierarchical structures. Hence, through this systematic study, for the first time we have conclusively shown the role of the fish's mucus layer to generate superoleophobicity and negate the common notion that hierarchical structure is the only reason for such intrinsic behavior of the fish scales.

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Related in: MedlinePlus

Measurement of contact angle on fish scales.(a) Silicon oil drops, used as model fluid, resting on fish scales kept under water in a glass cuvette. (b) Technique used to achieve under-water needle-free drop deposition of silicon oil on soft deformable fish scale surface. (c) Commonly used procedure of contact angle measurement which inaccurately quantifies the static contact angle by using normal DSA 100 set-up due to unresolved drop base contact area. (d) Accurate quantification of contact angle using an additional illumination arrangement and modified experimental set-up. This figure was drawn by PRW.
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f4: Measurement of contact angle on fish scales.(a) Silicon oil drops, used as model fluid, resting on fish scales kept under water in a glass cuvette. (b) Technique used to achieve under-water needle-free drop deposition of silicon oil on soft deformable fish scale surface. (c) Commonly used procedure of contact angle measurement which inaccurately quantifies the static contact angle by using normal DSA 100 set-up due to unresolved drop base contact area. (d) Accurate quantification of contact angle using an additional illumination arrangement and modified experimental set-up. This figure was drawn by PRW.

Mentions: One of the key challenges in measuring the static contact angle for substrates like fish scale under-water is to have a mechanism in place where the needle producing the desired oil droplet (for pendant drop technique15) does not remain attached to the drop once it is brought in close contact to the characterizing substrate, i.e., fish scales. When the needle is attached to the drop, it creates additional force on the drop-substrate combination, which further spreads the drop on the substrate, thereby providing erroneous contact angle values35. Our recent under-water needle-free drop deposition technique15 overcomes this limitation by bringing in an additional oil-water interface (as shown in Fig. 4(b) with canola oil used at the interface between water and air) and hence this has been used for accurate estimation of the static contact angle of oil drop on fish scales kept under water, for both with and without mucus, as shown in Fig. 4 (a). This accurate measurement of contact angle is more critical in this case as fish scale with or without mucus is essentially a soft deformable substrate (soft matter) and hence any force exerted by the traditional needle-drop assembly on the characterizing substrate during the contact angle measurement (as done in conventional pendant drop method) will generate additional stresses on the substrate, which will result in erroneous contact angle value, which has often been the case so far4511.


Under-water superoleophobicity of fish scales.

Waghmare PR, Gunda NS, Mitra SK - Sci Rep (2014)

Measurement of contact angle on fish scales.(a) Silicon oil drops, used as model fluid, resting on fish scales kept under water in a glass cuvette. (b) Technique used to achieve under-water needle-free drop deposition of silicon oil on soft deformable fish scale surface. (c) Commonly used procedure of contact angle measurement which inaccurately quantifies the static contact angle by using normal DSA 100 set-up due to unresolved drop base contact area. (d) Accurate quantification of contact angle using an additional illumination arrangement and modified experimental set-up. This figure was drawn by PRW.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4264028&req=5

f4: Measurement of contact angle on fish scales.(a) Silicon oil drops, used as model fluid, resting on fish scales kept under water in a glass cuvette. (b) Technique used to achieve under-water needle-free drop deposition of silicon oil on soft deformable fish scale surface. (c) Commonly used procedure of contact angle measurement which inaccurately quantifies the static contact angle by using normal DSA 100 set-up due to unresolved drop base contact area. (d) Accurate quantification of contact angle using an additional illumination arrangement and modified experimental set-up. This figure was drawn by PRW.
Mentions: One of the key challenges in measuring the static contact angle for substrates like fish scale under-water is to have a mechanism in place where the needle producing the desired oil droplet (for pendant drop technique15) does not remain attached to the drop once it is brought in close contact to the characterizing substrate, i.e., fish scales. When the needle is attached to the drop, it creates additional force on the drop-substrate combination, which further spreads the drop on the substrate, thereby providing erroneous contact angle values35. Our recent under-water needle-free drop deposition technique15 overcomes this limitation by bringing in an additional oil-water interface (as shown in Fig. 4(b) with canola oil used at the interface between water and air) and hence this has been used for accurate estimation of the static contact angle of oil drop on fish scales kept under water, for both with and without mucus, as shown in Fig. 4 (a). This accurate measurement of contact angle is more critical in this case as fish scale with or without mucus is essentially a soft deformable substrate (soft matter) and hence any force exerted by the traditional needle-drop assembly on the characterizing substrate during the contact angle measurement (as done in conventional pendant drop method) will generate additional stresses on the substrate, which will result in erroneous contact angle value, which has often been the case so far4511.

Bottom Line: We have identified the distinct chemical signatures that are responsible for such large contact angle, thereby making fish scale behave highly superoleophobic inside the water medium.In absence of the mucus layer, it is found that the contact angle decreases quite dramatically to around 150°, making it less oleophobic, the degree of such oleophobicity can then be contributed to its inherent hierarchical structures.Hence, through this systematic study, for the first time we have conclusively shown the role of the fish's mucus layer to generate superoleophobicity and negate the common notion that hierarchical structure is the only reason for such intrinsic behavior of the fish scales.

View Article: PubMed Central - PubMed

Affiliation: University of Alberta, Edmonton, Alberta, Canada.

ABSTRACT
Recent surge in the development of superhydrophobic/superoleophobic surfaces has been motivated by surfaces like fish scales that have hierarchical structures, which are believed to promote water or oil repellency. In this work, we show that the under-water oil repellency of fish scales is entirely due to the mucus layer formation as part of its defense mechanism, which produces unprecedented contact angle close to 180°. We have identified the distinct chemical signatures that are responsible for such large contact angle, thereby making fish scale behave highly superoleophobic inside the water medium. In absence of the mucus layer, it is found that the contact angle decreases quite dramatically to around 150°, making it less oleophobic, the degree of such oleophobicity can then be contributed to its inherent hierarchical structures. Hence, through this systematic study, for the first time we have conclusively shown the role of the fish's mucus layer to generate superoleophobicity and negate the common notion that hierarchical structure is the only reason for such intrinsic behavior of the fish scales.

Show MeSH
Related in: MedlinePlus